244 
Avgas persicus 
great sinus, coinciding in position with the origins of the pedal nerves, 
four arterial trunks open (see Text-fig. 4), and run outwards, one to 
each of tlie legs. The nerves lie free, each within the lumen of the 
corresponding artery. The anterior portion of the periganglionic sinus 
is continued in the form of a cylindrical sinus which, for distinction, 
may be termed the peripharyngeal sinus. The pheripharyngeal sinus 
encloses the oesophagus and pharynx and also the nerve trunks which 
supply the parts of the capitulum, and extends in the basis capituli 
almost to the buccal cavit 3 ^ Near its proximal end, a pair of arterial 
trunks arise from its dorsal wall and pass directly upwards to enter the 
posterior exti'emities of the chelicerae (see Text-fig. 5). Like the pedal 
trunks, these cheliceral arteries contain within their lumina the cheliceral 
nerves. At its distal extremity the periganglionic sinus apparently 
Fig. 5. Argas persicus c?. Transverse section of the peripharyngeal sinus at the 
place of origin of the cheliceral arteries, x 150 diam. 
divides into right and left branches, each of which enters the base of 
the corresponding palp. We have not been able to define a postero¬ 
median arterial trunk, but at the point where the splanchnic nerves 
issue from the brain, the periganglionic sinus in all probability gives 
rise to such a vessel. 
The walls of the sinuses and vessels are formed of an exceedingly 
thin membrane which presents the appearance of a flattened epithelium. 
From the foregoing description it is seen that the central and peri¬ 
pheral nervous systems are continually laved by the blood-stream which 
is directly propelled by the contractions of the heart, and further, the 
